1. Field of the Invention
The present invention relates to a prismatic battery having a cooling structure and a battery pack using the same, and more particularly to a prismatic battery and a battery pack in which each of the prismatic batteries are equally cooled when the battery pack is constituted such that the plurality of prismatic batteries are arranged in parallel and integrally bound together.
2. Description of Related Art
As a method for cooling a battery pack in which a plurality of prismatic batteries are arranged in parallel and integrally bound, it is known that the plurality of prismatic batteries are integrally bound while passages for a cooling medium are provided between them so that each prismatic battery is directly cooled by distributing the cooling medium through the passages. However, there is a problem that it is difficult to distribute the cooling medium equally through the respective passages.
Thus, as disclosed in Japanese Laid-open Patent Publication No. 8-148187, there is proposed an indirect cooling method in which a heat transfer plate is arranged between the plurality of prismatic batteries so as to be in contact with the prismatic batteries arranged in parallel and the heat transfer plate is cooled by a heat exchanger or the like.
Description will be made referring to FIG. 5. A plurality (ten in the drawing) of prismatic batteries 32 are arranged in parallel. A heat transfer plate 33 the cross section of which is T shape or L shape has a first heat transfer face 33a and a second heat transfer face 33b arranged at right angle to the first heat transfer face. The first heat transfer face 33a of the heat transfer plate 33 is inserted between the prismatic batteries 32 and 32 and the prismatic batteries 32 are bound together by end plates 34 provided at both ends thereof and fixed by binding bands 35 and thus, a battery pack 31 is provided. Each prismatic battery 32 is cooled by facing the second heat transfer face 33b of the heat transfer plate 33 to one side face of the battery pack 31 and bringing the second heat transfer face 33b into contact with a heat transfer face of a heat exchanger or with a cooling medium.
However, there is a problem in the above-mentioned structure for cooling the battery pack. That is, a binding force of the battery pack 31 integrally bound by the end plate 34 and the binding band 35 is reduced in accordance with creep deformation of the battery case of each prismatic battery 32 occurring with the lapse of time. Consequently, the contact between the heat transfer plate 33 and the battery case of the prismatic battery 32 becomes unstable, which generates imperfect contact points between the heat transfer plate 33 and the battery case of the prismatic battery 32. Since the efficiency of heat transfer is immediately lowered at the imperfect contact points, the cooling capability is substantially lowered overall and the temperature of the prismatic batteries varies widely. Thus, there is not provided sufficient long-term reliability.
In addition, when the prismatic batteries are cooled by bringing the second heat transfer face 33b of the heat transfer plate 33 into contact with the heat transfer face of the heat exchanger, the contact is not sufficiently secured because of camber of the heat exchanger or variation in disposed position and dimension of the prismatic batteries. Accordingly, there is a disadvantage that the cooling capability is not stable.